The instant invention relates to flow metering devices of the pressure differential producing type and more particularly to a venturi-type flow metering device which is operative with minimum fluid energy losses.
The use of venturi-type flow metering devices is extremely well known, and a wide variety of such devices have heretofore been available. The classic venturi tube is exemplary of one such device and comprises an elongated tubular member having a substantially straight inlet section, an elongated converging section of gradually reducing cross section, a substantially straight throat section, an elongated downstream diverging section of gradually increasing cross section and inlet and throat pressure sensing taps for sensing the static pressures in the inlet and throat sections, respectively. By applying the differential pressure between the inlet and throat taps in a flow equation, the rate of flow of a fluid through the device can be determined. Classical venturi tubes of this type have proven to be effective for metering the flow rates of both liquids and gases. Further, classical venturi tubes can be effectively used for metering the flow rates of fluids containing suspended or entrained solids since they do not easily become fouled and, in fact, exhibit somewhat of a self-scouring effect. However, while classical venturi tubes have proven to be effective for metering fluid flow rates, they have been characterized by relatively long laying lengths, and, therefore, they have generally been relatively expensive to manufacture compared to other known flow metering devices.
In addition to the classical venturi tube, a device known as the venturi nozzle is also widely used in flow metering applications. A venturi nozzle has a substantially straight inlet section, an elliptical converging section of reduced length, and a substantially straight throat section. A venturi nozzle can be constructed with a substantially shorter laying length than a comparable classical venturi tube. However, in a venturi nozzle, the inlet end of the converging section extends substantially perpendicularly inwardly from the inlet section and then extends arcuately in a downstream direction. The inlet end of the converging section of a venturi nozzle therefore acts somewhat like a dam which tends to trap solids which are suspended or entrained in a fluid passing therethrough. Hence, the venturi nozzle does not have the self-scouring effect found with classical venturi tubes.
Another flow metering device of the differential producing type is commonly known as the universal venturi tube and is disclosed in the U.S. patent to Halmi No. 3,686,946. The universal venturi tube comprises a substantially straight inlet section, an inlet cone which extends inwardly in converging relation from the inlet section, a throat cone which extends in converging relation from the inlet cone at a reduced angle relative to the inlet section, and a substantially straight throat section. Pressure sensing taps are also provided in the inlet and throat sections of a universal venturi tube for sensing the static pressures in these areas. The intersections between the inlet and throat cones and between the throat cone and the throat section are preferably both of substantially sharp configurations so that preferably at least two vena contractas are formed in a fluid passing through the device. The universal venturi tube has a self-scouring effect similar to the classical venturi tube, it can be constructed with a reduced laying length, and it is operative for providing accurate flow measurements. However, the energy losses in a fluid passing through the converging section of a universal venturi tube are substantially greater than the energy losses in fluids passing through the converging sections of comparable venturi tubes or venturi nozzles.
The instant invention provides a novel flow metering device of the venturi type which has advantages over all of the above-mentioned devices. The device of the instant invention can be constructed in a reduced laying length, it has a self-scouring effect, it has minimal energy losses, it provides accurate flow measurements, and it can be constructed with reduced manufacturing costs. The device of the instant invention comprises a shaped tubular member comprising a substantially longitudinally extending inlet section, a converging section which extends in converging relation from the inlet section, a substantially longitudinally extending throat section, and preferably also a downstream diverging section. The converging section comprises an inlet cone portion which extends angularly inwardly relative to the inlet section and a throat cone portion which extends angularly inwardly from the inlet cone portion to the throat section, the inlet cone portion, however, being at a reduced angle relative to the inlet section. An important feature in the device of the instant invention which distinguishes it from the devices of the prior art, in particular the universal venturi tube, is the provision of rounded intersections between the inlet cone and throat cone portions and between the throat cone portion and the throat section. These rounded intersections are provided to prevent the formation of vena contractas in a fluid passing through the device so that energy losses in the fluid are minimized. As a result of the rounded intersections in these areas, the energy losses experienced in the device of the instant invention are substantially less than those realized with the universal venturi tube. The device of the instant invention has a self-scouring effect similar to that found in a universal venturi tube, it can be constructed in a reduced laying length, and it is operative for providing accurate flow measurements. The device of the instant invention can be manufactured economically because of its reduced laying length, and further reductions in manufacturing costs can be realized as a result of the rounded intersections hereinabove described, rounded intersections being substantially easier to form in machining operations than the sharp intersections provided in the known devices of this kind. Accordingly, the device of the instant invention is economical to manufacture, and it is operative with minimum energy losses.
Other flow metering devices of the pressure differential producing type which represent additional prior art with respect to the instant invention of which the applicant is aware are disclosed in the U.S. Pat. Nos. to Schroder 2,863,318; Terrell 2,868,012; Shaffer 2,872,810; O'Keeffe 3,013,432; Halmi 3,733,902; Halmi 3,733,901; Bradham 4,174,734; and the British patent to Nathan 473,562. While these references teach a variety of flow metering devices, they do not teach the specific novel features of the instant invention hereinabove set forth, and hence they are believed to be of nothing more than general interest.
Accordingly, it is a primary object of the instant invention to provide an effective flow metering devices of the pressure differential producing type which is operative with minimum energy losses.
Another object of the instant invention is to provide a flow metering device which is operative with reduced energy losses and which has a self-scouring effect.
A still further object of the instant invention is to provide a flow metering device which is operative with reduced energy losses and which can be manufactured relatively inexpensively.
An even further object of the instant invention is to provide a flow metering device having inlet, converging and throat sections wherein the converging section comprises an inlet cone portion which extends angularly inwardly relative to the inlet section and a throat cone portion which extends angularly inwardly from the inlet cone portion to the throat section at a reduced angle relative to the inlet portion, and wherein the intersections between the inlet cone portion and the throat cone portion and between the throat cone portion and the throat section are of rounded configurations to prevent the formation of vena contractas in the device.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.